The thermoelectric effect is the generation of an electrical voltage from a temperature gradient in a solid material due to the diffusion of free charge carriers from hot to cold. More specifically, when a temperature gradient is applied across a solid material with free electronic carriers, a voltage gradient arises as carriers migrate from the hot side to the cold side. The strength of this thermoelectric effect is characterized by the Seebeck coefficient S, defined as the ratio between the voltage difference ΔV and the temperature difference ΔT. The absolute value of S is referred to as the thermopower. Finding materials with large thermopower can be vital for the development of thermoelectric generators and thermoelectric coolers, devices which can transform waste heat into useful electric power, or electric current into cooling power.